生土地种植苜蓿后土壤速效养分与pH值的时空变化

Spatio-temporal variability of soil available nutrients and pH value in raw soil after planting alfalfa

【目的】为评价苜蓿对改良土壤、培肥地力及草田轮作的影响提供依据。【方法】在苜蓿各生育期对0~60 cm土层进行取样，研究土壤速效养分含量和pH值的动态变化。【结果】种植苜蓿第2年各土层土壤硝态氮含量增幅较小，第3年各土层土壤硝态氮含量增幅较大，与种植前相比，其0-20、20-404、0-60 cm土层硝态氮含量分别增加了3.85，5.82和8.25 mg/kg;在第2年，各土层土壤速效磷含量变化呈抛物线型，于第2茬达到峰值。在第3年，头茬苜蓿生育期内各土层土壤速效磷含量均迅速下降，与种植前相比，0-20、20-40、40-60 cm土层土壤速效磷含量分别降低了3.16，2.98和2.40 mg/kg;各土层土壤速效钾含量逐年下降，与种植前相比，种植苜蓿后的第3年，0-20、20-40、40-60 cm土层土壤速效钾含量分别下降了94.35，88.29和88.55 mg/kg;各土层土壤的pH值略有增加，与种植前相比，种植苜蓿后的第3年，0-20、20-40、40-60 cm土层土壤的pH值分别增加了0.14，0.12，0.04。【结论】种植苜蓿后，土壤硝态氮含量呈先降低后升高的变化趋势，在第2年第1茬初花期时达到最低，苜蓿的固氮作用从第2年第2茬开始显现;土壤的速效磷含量变化呈抛物线型变化，于第2年第2茬达到峰值;土壤速效钾含量逐年下降;pH值略有增加但变化不明显。

[Objective] The basis was provided for evaluating effects of alfalfa on improving soil,enrie hing fertility and alfalfa crop rotations. [Method] According to different growth periods of alfalfa,soil of 0--60 was sampled,and dynamic changes of available nutrients and pH value in each layer of raw soil were studied. [Result] The results showed that in the second planting year,the content of nitrite nitrogen in creased slowly in each layer;in the third planting year,nitrite nitrogen content rose in each layer. Compared with planting alfalfa,the layer of 0--20,20--40,40--60 em was increased 3.85,5.82,8.25 mg/kg. In the second planting year,soil available P content varied in each layer in a shape of parabola. In the 1st stubble of the third planting year, the content of available P declined rapidly. Compared with planting alfalfa, the a- vailable P in 0--20,20--40,40--60 cm respectively dropped 3.16, 2.98 and 2.40 mg/kg. Available K con tent in each layer decreased year by year. Compared with planting alfalfa,in the third planting year,the available K in 0-20, 20-40,40-60 cm lowered respectively 94.35,88.29 and 88.55 mg/kg, pH value in creased slightly. Compared with planting alfalfa, in the third planting year. pH value in 0--20,20--40,40-60cm increased respectively 0.14,0.12,0. 04. [Conclusion] By planting alfalfa,the nitrite nitrogen content increased at first and then decreased,the minimum occurred in the 1st stubble of the second planting year. Nitrogen fixation began to emerge in the 2nd stubble of the second planting year. Available P content varied in a shape of parabola and got its peak volume at the 2nd stubble of the second planting year. The content of available K decreased year by year. pH value increased slightly, but the change was very small.